Managing flame direction (Cycles)
Overview:



You can control flame direction by Normals from Mesh that is your Flow object. In this example I'm using Circle filled with Triangle fan.

Mesh:



As I said before, simple Circle. You can check where Normals direction will go in Edit Mode > Mesh Display tab > Normals.

Flow:

Now in Flow settings you'll need to turn on Initial Velocity. Set Source to 0 and Normal to something higher then 0. This value will control the initial flame speed. By now flame will be rising but we can change it in Domain settings easily.



Domain:

In Domain settings you will need to set Temp. Diff. to 0. This will make flame straight. Higher value = faster smoke rising.